Circumferential chambers of the above type are generally provided in the region of the inflow or the outflow of turbomachines, for example turbines, expanders or compressors. Whereas the region of the rotating flow guide contours, for example of the rotor blades or of the impeller, is optimized to the greatest possible extent in terms of flow, disproportionately high flow losses still frequently occur in the surrounding regions. In order to counter this, the 90° deflection generally required in the region of an inflow or outflow has already no longer been formed as a simple incoming radial flow into an annular chamber, but instead as a preferably tangential inflow to a collecting chamber tapering in the circumferential direction, this also being referred to as incoming spiral flow or outgoing spiral flow.
The size and the non-rotationally symmetrical shape of the collecting chamber mean that the conditions for chip-forming machining of this component are unfavorable, and therefore this component is generally formed as a cast structure. A structure for material-removing production has nevertheless been provided for those sizes where the solid material is available for such a collecting chamber, since the strong dependence on suppliers for cast parts is a major economic disadvantage. Structures of this type generally have a two-part form so as to avoid undercuts during the chip-forming machining. Accordingly, there is an outer shell part and an inner contour insert, which is inserted into the outer shell part and thereby forms a collecting chamber enclosed by the two components. Said collecting chamber generally has an axial, first flow opening, which extends in the circumferential direction, and a second flow opening, which is designed for radial flows.
In the case of a centrifugal compressor, the compressed gas passes, by way of example, from the impeller into a radially oriented annular chamber and then regularly into the collecting chamber after a 90° deflection. In order to avoid turbulence, said collecting chamber is formed with a cross section which widens along the circumferential direction, such that the maximum cross section is located in the region of a radial outflow or the second flow opening where all of the outflowing or inflowing fluid finally collects to form a throughflow. In virtually all cases, this second flow opening is adjoined by a diffuser which feeds the process gas, for example in the case of the compressor, to a further compressor stage, for intermediate cooling or for another process. At the outlet from the collecting chamber into the diffuser, extremely disadvantageous flow losses occur in the case of the milled structure.
DE 1 291 943 B, FR 1300622 A, DE 3040747 A1, EP 1586745 A1 and DE 19640647 A1 each disclose turbomachines having collecting chambers. DE 3040747 A1 discloses a collecting chamber made of hard white cast iron having a round cross section which widens in the circumferential direction. The cast component is very complex and results in a costly and unfavorable dependence of the machine manufacturer on the supplier of the cast parts.
Proceeding from the embodiment of a collecting chamber defined in the introduction, the invention is based on the object of providing a collecting chamber which, in particular in the region of the second flow opening, has only small flow losses and is nevertheless not a cast structure.